interface IPerson {
   name: string;
   age: number;
   eat: (food?: string) => void;
}

interface IStudent extends IPerson {
   major: string;
   study: (major: string) => void;
}

const zs: IStudent = {
   name: "",
   age: 0,
   major: "",
   eat: function (food?: string | undefined): void {},
   study: function (major: string): void {},
};